Various types of mechanical fasteners are known for holding articles together, such as hook and loop type fasteners or complementary pairs of fasteners that engage with one another. The complementary pairs of fasteners typically have functional surfaces with headed stems with heads for engaging the two fasteners together. The engaging stems are located in ordered positions relative to one another on a substrate. The patterns usually consist of straight rows of equally spaced engaging stems. Examples of fasteners with straight rows of engaging stems are U.S. Pat. No. 3,101,517, "Fastener," (Fox et al.) and U.S. Pat. No. 4,290,174, "Separable Fastener and Article for Making Same" (Kalleberg). When the fasteners are engaged, the stems of each resiliently deflect to allow the heads to enter the space between the adjacent stems of the other fastener.
It has also been know that straight rows of engaging stems may allow the individual fasteners to move relative to each other in a direction parallel to the rows of the fasteners, also referred to as shear slip. As a result, improved ordered patterns of engaging stems were developed to decrease the probability of the fasteners moving in the shear direction. Examples of fasteners with such ordered patterns are U.S. Pat. No. 5,625,929 "Interengaging Fastener Member," (Hattori et al.) and U.S. Pat. No. 5,040,275, "Strip Material Used for Forming Fasteners," (Eckhardt et al.).
U.S. Pat. No. 3,408,705, "Fastener Articles," (Kayser et al.), discusses fasteners comprising pairs of unitary interengaging articles. Each article has a base carrying a multiplicity of headed engaging elements over its surface. The positions of the element heads are unordered with respect to each other. This lack of order makes the engagement force of the articles much more uniform at all relative angles and positions of engagement than if the elements were ordered.
FIG. 1 is an example of a prior art mechanical fastener 19. Mechanical fastener 19 includes a substrate 22 and a plurality of engaging stems 28 extending from the substrate 22 in an ordered arrangement. The substrate 22 includes a first major surface 24 and a second major surface 26 opposite the first major surface 24. The engaging stems 28 extend from the first major surface 24 of the substrate 22. The engaging stems include a stem 30 and a head 32 on the stem 30 opposite the first major surface 24 of the substrate. Typically, the ordered arrangement of the engaging stems 28 is an arrangement of a plurality of lateral and longitudinal rows of engaging stems 28 on the substrate 22. Mechanical fastener 19 is designed to engage with loop material or interengage with another mechanical fastener of the same or compatible design, as shown in FIG. 2.
FIG. 2 illustrates a pair of the mechanical fasteners 19, 19' of FIG. 1 interengaged with one another. Due to the ordered spacing of the engaging stems 28, the pair of fasteners 19, 19' must be first aligned such that the heads 32' of fastener 19' are positioned over the space between adjacent engaging stems 28 of fastener 20. Next, the fasteners 19, 19' are pushed together, slipping the heads 32' of mechanical fastener 19' between adjacent stems 30 of mechanical fastener 19 thereby engaging with the heads 32 of the adjacent stems 30. Typically, the engaging stems 28, 28' of fasteners 19, 19' are flexible to allow for the slippage of the heads 32, 32' between adjacent stems 28, 28'. As a result, the mechanical fasteners 19, 19' interengage and are held in place by their respective engaging heads 32, 32'.